Effectiveness of EVOH has been recognized in the field of wrapping films for foodstuffs, etc., especially for purposes of wrapping foodstuffs requiring barrier properties against oxygen, other products requiring retention of flavor, and the like. However, a film composed of EVOH alone is inadequate both in toughness and in barrier properties against water and moisture.
In order to attempt to overcome these inadequacies, EVOH has been used in the form of a multilayered structure obtained by laminating a thermoplastic resin such as polypropylene, polystyrene, etc. and various heat sealant layers represented by ionomers, ethylene-vinyl acetate copolymers, etc.
In the case where multilayered structures (films, sheets, parisons, etc.) prepared by various methods are subjected to fabrication into containers, etc., particularly in the case where drawing is performed at a temperature lower than the melting point of EVOH, small voids, cracks, localized non-uniform sections, etc. are often formed in the EVOH layer so that the oxygen barrier properties of a container so formed are seriously reduced. In addition, the container does not exhibit an esthetic appearance. Accordingly, under these circumstances, EVOH can not be used as containers for foodstuffs, etc.
In order to prevent pinholes, cracks, etc. in the EVOH layer, formed upon hot drawing, research has included incorporating various plasticizers into EVOH (Published Unexamined Japanese Patent Application Nos. 88067/78 and 20345/84), blending polyamide resins with EVOH (Published Unexamined Japanese Patent Application Nos. 141785/77 and 54755/83, 36412/83), etc. In any case, however, satisfactory results were not obtained. In order to improve the hot drawing properties of the EVOH using plasticizers represented by those containing hydroxy groups and the aromatic sulfonamide type, etc., it is necessary to incorporate 10 to 20 parts by weight of the plasticizers per 100 parts by weight of EVOH. In such case, many problems result, such as reduction in gas barrier properties, reduction in the adhesion strength of the EVOH layer to other resin layers perhaps due to bleeding of the plasticizers, etc. Therefore, such a system is inadequate.
Methods comprising blending polyamide resins with EVOH to impart flexibility thereto and improve fabrication properties are known. Many patent applications directed thereto have been filed (Published Examined Japanese Patent Application Nos. 24277/69 and 24813/85, Published Unexamined Japanese Patent Application No. 129035/83, Published Examined Japanese Patent Application No. 38897/84, Published Unexamined Japanese Patent Application No. 36412/83, etc.). However, use of polyamides, which may improve hot draw formability at a high speed, produce formed products in which a number of gel-like matters are present, perhaps due to a rapid chemical reaction with EVOH. Also, due to marked coloration, the polyamides have generally been found unsatisfactory for use.
Published Unexamined Japanese Patent Application Nos. 161453/85 and 163952/85 directed to the system of blending a polyamide resin having less gel and relatively less coloration and EVOH have also been published. Although it appears that hot drawing at a low speed would produce well formed products free from cracks, pinholes, non-uniform sections, etc., from their appearance, however, probably due to insufficient compatibility with EVOH, the system produces, as observed by measurement of the gas barrier properties, extremely variable data. It is suspected that the presence of minute pinholes that are hardly discernible by the naked eye are responsible. Furthermore, with the speed up of a hot drawing machine, the variation in the measurement data of gas barrier properties is greatly increased. The variation in data has resulted in reducing the reliability of these containers as ones with good gas barrier properties.
Therefore, an object of the present invention is to develop EVOH having good gas barrier properties and having good reliability as containers having such gas barrier properties, namely, to develop EVOH which does not form minute pinholes, cracks, non-uniform sections, etc. upon hot drawing at a high speed.